Field of the Invention
Embodiments of the present invention relate generally to a method for acquiring a parameter for correcting a dose of a charged particle beam, a charged particle beam writing method, and a charged particle beam writing apparatus. More specifically, embodiments of the present invention relate, for example, to an apparatus and method that correct resist heating.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 18 is a conceptual diagram explaining operations of a variable-shaped electron beam writing or “drawing” apparatus. The variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
With development of the optical lithography technology and shorter wavelengths due to EUV (extreme ultraviolet), the number of electron beam shots required for mask writing is acceleratedly increasing. On the other hand, for ensuring the line width accuracy needed for micropatterning, it is aimed to reduce shot noise and pattern edge roughness by making resist less sensitive and increasing the dose. Since the number of shots and the amount of dose increase limitlessly, the pattern writing time also increases limitlessly. Therefore, it is now considered/examined to reduce the writing time by increasing the current density.
However, if the substrate is irradiated with an increased amount of irradiation energy as higher density electron beams in a short time, another problem occurs in that the substrate overheats resulting in a phenomenon called “resist heating” of changing the resist sensitivity and degrading the line width accuracy. To solve this problem, there is considered and examined a method (heating correction) of calculating, for each minimum deflection region in a deflection region, a representative temperature of the minimum deflection region concerned based on heat transfer from other minimum deflection regions written prior to the current one, and of modulating the dose by using the representative temperature (refer to Japanese Patent Application Laid-open (JP-A) No. 2012-069675).
On the other hand, in the electron beam writing, when writing a circuit pattern by irradiating a mask, coated with resist, with electron beams, a phenomenon called a “proximity effect” occurs due to backscattering of the electron beams penetrating the resist film, reaching the layer thereunder to be reflected, and entering the resist film again. Thereby, a dimensional change occurs, that is, a written pattern is deviated from a desired dimension. In order to avoid this phenomenon, a proximity effect correction operation that suppresses such dimensional change by modulating the dose is for example performed in the writing apparatus.
The dose modulation against the resist heating described above is performed in consideration of the temperature at the time of an electron beam shot of interest (target shot, shot concerned). Therefore, temperature is not considered with respect to calculation for correcting the proximity effect generated by backscattering by another shot at the peripheral position different from that of the shot of interest (target shot). Accordingly, when the heating effect of the backscatter is large, there is a problem in that the correction error is large in the conventional calculation model. Therefore, it is desirable to correct the heating effect with respect to a backscattered electron at the time of exposure. However, conventionally, a sufficient correction method has not been established.